package lanqiao;

/**
 * @Project : AlgorithmLearning
 * @Package : LanQiao.PrepareForCompetition
 * @File : Q0174.java
 * @Author : WangRuoyu
 * @Date : 2023/3/20 14:28
 */

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Q0174 {
    static void quickSort(int[] q, int l, int r) {
        if (l == r) {
            return;
        }

        int x = q[l];
        int i = l - 1;
        int j = r + 1;

        while (i < j) {
            while (q[++i] < x) ;
            while (q[--j] > x) ;
            if (i < j) {
                int t = q[j];
                q[j] = q[i];
                q[i] = t;
            }
        }
        quickSort(q, l, j);
        quickSort(q, j + 1, r);
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] words = br.readLine().split(" ");

        int n = Integer.parseInt(words[0]);
        long s = Long.parseLong(words[1]);

        int[] money = new int[n];
        words = br.readLine().split(" ");
        for (int i = 0; i < n; ++i) {
            money[i] = Integer.parseInt(words[i]);
        }

//        Arrays.sort(money);
        quickSort(money, 0, money.length - 1); // 自己写的快排会快一点

        double ss = 0;
        double aver = (s * 1.0) / n;
        double averm = aver;
        int i;
        for (i = 0; i < n; ++i) {
            if (money[i] < averm) {
                s -= money[i];
                averm = (s * 1.0) / (n - 1 - i);
                ss += (aver - money[i]) * (aver - money[i]);
            } else {
                break;
            }
        }
        ss += (n - i) * (averm - aver) * (averm - aver);
        System.out.printf("%.4f", Math.sqrt(ss / n));
    }
}